Automatic pilot



Dec. 15, 1953 w. L. HUNTINGTON AUTOMATIC PILOT Filed Oct. 8. 1948 IF, wzomm.. E Pr g- I du. @mwm Nm INVENTOR. WILUAM L.HUNT\NGTON WM M alim/16g.

Patented Dec. 15, 1953 AUTOMATIC PILOT William L. Huntington, Minneapolis, Minn., as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application October 8, 1948, Serial No. 53,472

13 Claims.

This invention pertains to automatic control apparatus for dirigible craft which apparatus when applied to an aircraft is termed an automatic pilot.

This invention is an improvement in the type of automatic pilot disclosed in the United States application of John F. Schoeppel, Serial No. 567,254, led December 8, 1944. In the aforesaid application of John F. Schoeppel, provision is made for operating the aileron, rudder, and elevator of an aircraft by individual servomotors. Each servomotor is operated by an amplifier which has a balanceable control circuit.

When the aircraft is manually flown, at which time the servos are disassociated from the control surfaces, each amplifier controls a centering motor which in turn drives means to rebalance the amplifier control circuit during any change kin the attitude of the aircraft while it is under manual control. ing motor for each of the three amplifier circuits.

It is an object of this invention to provide in such aforesaid automatic pilot a single centering motor common to the three amplifier circuits thereby reducing the number of motors required.

It is a further object of this invention to provide in such aforesaid automatic pilot a single motor and a plurality of gear trains selectively connectible with said motor, each gear train being associated with an amplifier input circuit.

A further object of this invention is to provide for manual control of said gear trains and motor connection while said automatic pilot controls an aircraft.

A further object of this invention is to provide for a change of gear ratios in said gear train when said automatic pilot controls an aircraft.

These and further objects of the invention will be evident upon consideration of the accompanying description and drawing disclosing a preferred embodiment of the invention.

The sole ligure is a schematic arrangement of the improved automatic pilot.

Referring to the drawing, there is disclosed therein an arrangement for operating the ailerons, rudder, and elevator of an aircraft whereby three axis control of the aircraft is provided. The ailerons (not shown) are connected to cables Ii! extending from a cable drum II which is The shaft I2 is oper- There is an individual centerrelay lead 46.

The amplifier I'I is controlled by a balanceable network 20. The control network 20 is itself operated by a directional gyro T4, a vertical gyro l0, a centering and trim drive 80, and a rebalancing drive I2 operated by the aileron servomotor I4.

The servomotor I4 reversibly positions the cable drum I I. The aileron servomotor I4 may be of the type disclosed in an application of Willis H. Gille, Serial No. 447,989, filed June 22, 1942, or like that disclosed in a patent to Willis H. Gille et al. 2,425,733. Extending from the aileron servomotor is a brake energizing lead 2I, a one rotation clutch lead 22, and an opposite rotation clutch lead 23.

The aileron engaged relay has an operating coil 24 and a plunger 25 associated therewith. Operably associated with said plunger are four pivoted single pole double throw single break switch arms 26, 2l, 28, and 29. Associated with the switch arms are contacts having the designated functions. Coacting with switch arm 26 is an in centering drive gear train contact 30 and an inoperative out contact 3|. Coacting with switch arm 2l is an in servo brake solenoid contact 32 and an inoperative out contact 33. Coacting with switch arm 23 is an in servomotor one clutch coil contact 34 and an out one rotation centering drive contact 35. Coacting with switch arm 29 is an in other servomotor clutch contact 3S and an out opposite centering drive rotation contact 31.

The amplifier Il is provided with power input connections 40, 4I which may be connected to the ships supply. The amplifier I'l additionally includes signal input connections 42, 43 which are connected to the input control network 26; D. C. supply lead 44, left relay lead 45 and right The amplifier Il may be of the type disclosed in the aforesaid patent to W. H. Gille et al. or that disclosed in the aforesaid application of Willis H. Gille. Such amplifier has a pair of relays alternatively operated dependent on the phase of a control signal across connections 42, 43. A relay is continuously or intermittently operated dependent on the magnitude of a control signal. Associated with the two relays are conductors or leads 45, 46. In such an arrangement either relay lead 45 or 46 is energized depending upon the phase relationship between the voltage across the power input leads 4I), 4I and that across the signal input leads 42, 43.

The network 2U includes a variable impedance bridge network 5i) and a variable impedance bridge network et. The bridge network 5@ includes a rebalancing potentiometer 5| having a resistor 52 and a slider 53 a centering-trim drive potentiometer 5s having a resistor 55 and a slider' 56; and a transformer iii having a primary winding 58 and a secondary winding 59, Resistor 52 is connected across the secondary winding 5t of the transformer 59. Slider 51% is operatively driven from the servomotor shaft l2 of aileron servoinotor ifi. Resistor 55 is connected across the secondary winding E9 in parallel with resistor 52. Slider de is operatively driven by a centering and trim drive gear train S0. Connection 52 extends from ampliiier to slider 53 of the rebalancing potentiometer 5|.

Bridge network 60 includes a vertical gyro banking potentiometer 6| having a resistor 62 and a slider 53; a directional gyro aileron potentiometer Sii comprising a resistor 65 and a slider $5; and a transformer lil comprising a primary winding 58 and a secondary winding 69. Since in the several networks the transformer secondary windings may have a common primary winding, the primary winding is indicated by the same reference character Resistor d2 is connected across the ends of secondary winding Se. The slider 53 is adjusted by the vertical gyro ii? through an operative connection l l. The vertical gyro l is of the type whose rotor rotates about a vertical axis and is supported about two horizontal axes which are respectively perpendicular to each other. The vertical gyro may be of the type disclosed in the aforesaid application of Willis H. Gill-e, 447,989. The vertical gyro le is so arranged in the aircraft that upon movement of `the aircraft about the roll axis the slider d3 is moved with respect to its resistor 62 by means of the vertical gyro lil. A lead connection 'l2 extends from slider 63 to slider 55 of potentiometer 53. The resistor 55 of potentiometer iid is connected across the secondary winding @d in parallel with resistor e2. The slider |55 is adjusted by a directional gyro 'it by a suitable operating connection l5. The directional gyro is of the type well known in the art whose rotor is mounted for rotation about a horizontal axis and is so supported that it may also rotate about a horizontal axis at right angles to its spin axis. In addition the rotor is supported so that it may rotate about a vertical axis. The directional gyro 'Hl is so mounted in the aircraft that the vertical axis is parallel with the vertical 'or turn axis of the aircraft. Upon movement of the aircraft about the turn axis due to changes in heading of the aircraft the directional gyro 'id will adjust the slider 65 with respect to resistor 05. A lead connection l extends from slider 55 to ground. The input circuit network is completed to the grounded lead 43 of amplifier ll.

As previously stated, the slider 56 of potentiometer 5d is operated by an aileron trim and centering drive S9 which is alternatively controlled with servomotor ifi by amplifier i7. The trim and centering drive t@ is powered by a motor 8| which may be either a D. C. or an A. C. motor of suitable type. The motor Si through its shaft 52 drives a reduction gearing 03. The speed reduction gearing 33 through its output shaft 8f3 drives a broad pinion 85. In mesh with the broad pinion S5 is a gear 855 loosely supported von a 1 hollow shaft e?. Also loosely carried by shaft 8l is a gear 8S which has a rotation opposite that of the gear being for this purpose driven from the pinion S5 through a reversing gear 8S. The gears 5t and 355 may be suitably supported against axial movement on the hollow shaft 87 by means not shown. The gears Se and S- carry opposed clutch faces .iii and 9i respectively. Carried by said hollow shaft 3'; is a clutch member S2 which is interposed between the clutch elements 90 and 9| for association therewith. The hollow shaft El carries two spaced armature pieces 93 and Q0. Wound concentric with the hollow shait Si and interposed between the armatures and 9d is a differential operating coil 05. The diierential coil S5 includes a coil 9d which coacts with armatureQS and a coil 97 which coacts with armature 94 whereby the shaft is axially moved so that the clutch element Si. is associated with or engages either the clutch face @d of gear i353 or the clutch face 0| of gear 8S. Shaft centralizing means illustrated as a flat spring Si@ is carried by a bracket Sii. The spring 98 extends into a circumferential slot m0 in hollow shaft The spring 93 tends to maintain shaft iii centralized so that the clutch element 92 centralized with respect to the clutch faces and e i.

A solid shaft 10| supports the hollow shaft 87. The shaft |0| and the shaft 81 may be keyed together by suitable splines (not shown). The shaft |05 carries a diierential arm |02. A shaft |03 is journalled in the free end of arm |02. Fixed to one end of shaft |03 is a gear |04 and fixed to the opposite end of said shaft is a gear 05. Gear i0@ meshes with a fixed gear 06 carried by a fixed bracket |01. The gear |05 meshes with a gear |08. The gear |08 is rotatably carried by a second hollow shaft |09. A clutch face is carried by one side of diierential arm |02. An opposing clutch face I3 is carried by the gear 08. Interposed between the clutch faces Il and I I3 is a clutched element l2 carried by the hollow shaft |09. The hollow shaft 109 carries an armature |4 which coacts with a coil |I5. The coil l5 is concentric with the hollow shaft |09. The shaft |09 is splined or keyed to a second solid shaft ||8 and is axially movable with respect thereto. Upon energization of the coil H5, the armature I4 is attracted toward said coil and moves the clutch element 2 into engagement with the clutch face H3 on gear |08. When the coil l5 is deenergized, a spring l5 interposed between the coil 5 and armature lill tends to move the clutch element ||2 to the left whereby it is engaged with the clutch face |l| carried by the diierential arm |02. The solid shaft H0 carries the slider 56 and for purposes of illustration in the drawing the slider has been rotated, as in similar instances, through an angle of 90 degrees into the main projection plane.

A trim drive which in the instance described begins with the gears 86 and 89 and terminates in shaft l I8 is duplicated in the rudder and elevator channels of the automatic pilot. In other words each trim drive in the rudder and elevator networks has a pair of gears corresponding with gears B and 39 of the aileron trim drive which mesh with the broad pinion and a terminal shaft corresponding with shaft 8. This engagement of the corresponding gears with the driving pinion 85 is indicated by an operative connection The coils 96 and 9i of dierential coil Q5 have an input connection |2| and |25 respectively and a common ground connection |24. The connection |2| extends to the out contact 31 of aileron engaged relay l5 and through a branch lead |22 to a contact |25 of a manually operable switch |30. The connection |25 extends to an operative out contact 35 of engaged relay I6 and through abi-"anch connection |28 to a contact |21 of switch |30.

The manually operable switch |30' includes a manually operable knob |3| which carries a switch blade |32 intermediate contacts |25, |21. A lead |35 extends from switch blade |32 to a bat tery |34. The opposite side of the battery is con'- nected to ground. A lead 38 extends from the battery |34 to the switch arms 26 and 21 of the aileron engage relay I6.

The operating coil ||5 of trim drive- 80 has one side connected through a lead |35 to in con-- tact 30 of aileron engage relay |6. The opposite side of the coil l5 is connected to ground.

The rudder and elevator channels of the auto;- inatic pilot have been illustrated in block dia'- grams for purpose of simplicity. The aileron channel of the automatic pilot has been described in detail. The rudder and elevator chan-'- nels have components which have their countere part in the aileron channel. These counterparts will be pointed out, and it is considered that the operativeness of the rudder and elevator channels will therefore be apparent.

The rudder channel includes cables 2 |J extend ing from the rudder servomotor cable drum 2| This drum 2|| is driven by a rudder servomotor 2M corresponding with the servomotor |4 of the aileron channel.v The rudder servomotor 2|4 is controlled by a rudder amplilier 2|1 through a :mi

rudder engage relay 2|6. The amplifier 2|1 and rudder engage relay 2|5 corresponding with the amplier |1 and the engage relay I6 of the aileron channel. The rudder amplier 2|1 has an input network circuit 220 corresponding with the input t circuit 20 of the aileron amplifier |1. This cir.` cuit 22D includes a bridge network 250 corresponding with the bridge 60 in the aileron channel and a bridge network 250 corresponding with the bridge 50 of the aileron channel.

The bridge network 260 includes a directional gyro rudder potentiometer whose slider is operated from the directional gyro 14 by operating means 15 in response to course deviations and a vertical gyro rudder compensating potentiometer operated by means 15 from the vertical gyro 10 in response to roll deviations.

The bridge network 250 includes a trim and centering potentiometer driven by a rudder trim drive 280 alternatively controlled with servomotor I, 2|4 by amplier 211 and corresponding with the trim drive 8|] of the aileron channel and also a servo balance potentiometer whose slider is op'` erated from the rudder lservomotor shaft extend ing from servomotor 2 4. The rudder channel in;- cludes a manually operable switch 23|! correa spending with the switch of the aileron channel. A manually operable switch 23|) may be used to additionally control trim drive 280 over that provided by ampliner 2|1.

The elevator channel includes a servo drum 3| which operates cables 3|0 extending to the ele' vator (not shown). Cable drum 3|| is operated from the elevator servomotor 3M which corresponds with the servomotor le of the aileron channel. The elevator ampliner 3|1 alternative'- ly controls a trim drive 3% or the servomotor', 3M through the elevator engage relay' 316. The elevator ampliiier 3|? is controlled bya control circuit which includes a bridge network and a bridge network 35B.- )l

The bridge network 35d includes a vertical gyr'o pitch potentiometer whose slider is operated through operating means 13 from vertical gy'io 10 upon movement of the aircraft about the 6 pitch axis. The network 360 includes a vertical gyro upelevator potentiometer whose slider is operated through connection 1| from the verti-v cal gyro 10 upon movement of the aircraft about the roll axis.

The bridge network 35D includes a centering and trim drive potentiometer whose slider is operated by the trim drive 385 and a servo balance' potentiometer whose slider is operated from the servomotor 3|4.

In addition to being automatically controlled by the amplifier 3|1 through the engage relay 3|`8, the trim drive 380 may be also controlled from a manually operable switch 333. The leads which extend from the manually operable switch 339 to the coils of the differential coil in trim drive 38! are shown in discontinuous forni for ease of illustration.

Having completed a detailed description of the components of the apparatus and their interrelationship, the operation of the apparatus will be' considered in connection with the flight of an aircraft in whifh it may be considered to be installed.

Consider initially the operation or the ampliner and its control network. By referring to the drawing, it is evident that the input circuit of each channel amplifier includes two networks in the forin oi a Wheatstone bridge. With respect to the aileron amplifier input circuit, the bridge has output elements thereof consisting of the andere and With respect to the bridge the output elements are the sliders 53 and 56. Normally the sliders are all at the electrical centers of their respective resistors at which time there is no dinerential or potential between the output elements of either bridge.

Should the aircraft change its heading, the slider 5S will be moved by the directional gyro depending on direction of devia-tion toward one or the other ends of resistor whereby a differential of potential will exist across the sliders 53 and 5G. the autopilot is engaged, will cause the operation of the ampliiier il and the servomotor 4 whereby the slider '53 will be positioned until the potential difference between sliders 53 and 5S is equal and opposite to that between sliders 63 and SG with the result that the input circuit of amplifier l1 is balanced.

On the other hand when the aircraft is being manually controlled in which case the control surfaces are directly manually actuated, the aileron, rudder, and elevator engage relays are in the out position. In the out position, as shown in detail in the aileron channel, the amplie'r output connections 45 and 66 are connected to the switch arrns 28 and 23 and out contacts 35 and 3? and leads |26 and |2| to the coils 91 and S5 of diiierential coil 95 respectively.

If the pilot should manually move the ailerons, he' simultaneously moves the slider 53 by rotating the drum through cables l0. The slider 53 in its adjusted position is at a potential different from that or slider 56 of potentiometer 54. The input circuit of aileron amplifier |1 is now unbalanced.

If the slider 53 be moved toward the left, the input circuit of ampliiier will be so unbalanced 'as to cause the operation of the relay con# nested to lead 45. D. C. voltage is now extended from the battery |34, through lead 4'4, to the con nection 45, the switch arm 28, out contact 35, lead |26,` coil 91, lead |24 to ground, and to the grounded side of battery |34. The coil 91 as Such diierence of potential, when i thus energized attracts the armature 94 and thus the hollow shaft 8l; The movement of the shaft is thus toward the left bringing the clutch element e2 into engagement with the clutch face 9i! of gear 86.

Since the gear 8S is being driven by the pinion 85 the shaft 87 will be rotated and will also rotate the solid shaft lili splined thereto. The solid shaft ll as stated carries the diiferential arm H32 bearing the clutch face l i l. In the out position of relay I5 the coil H is unenergized, consequently the hollow shaft H19 with its clutch elementv H2 is toward the left as shown in the drawing whereby motion of the differential arm is directly transmitted to the clutch element H2 and through the spline connection of the shaft It!) bearing the clutch element l i2 to the solid shaft HS which operates the slider 15E. The slider is moved toward the left to balance the amplifier input circuit.

As the aircraft banks under the manually applied aileron, the vertical gyro 'iii operates the slider 53 of the banking potentiometer iii to reverse the phase of unbalance of ampliiier Il. The slider Se is again positioned by the aileron trim drive d@ but in a reverse direction to mainn tain the input circuit of aileron amplifier il in balanced condition.

The movement of the vertical gyro it in response to the banking of the aircraft also causes the gyro 'i0 to displace the slider in the rudder network and a slider of the up elevator potentiometer in elevator bridge network In the rudder channel, the rudder trim drive Siti! is controlled by the amplifier 2 Il which had had its input circuit unbalanced by the vertical gyro l to eiect rebalancing of the input circuit of amplifier 2li.

In the elevator channel the operation of the slider in the up elevator potentiometer causes the imbalance or the input circuit of amplifier 3i?. The amplier 3H operates and causes the elevator trim drive 33D to operate the slider associated therewith in network 359 to rebalance the input circuit of amplifier 3H.

It is thus apparent that as the aircraft moves about the roll axis due to the manual operation of the ailerons, which movement results in the unbalance of the input circuit of the aileron, the

rudder, and the elevator amplifiers, that such input circuits are again rebalanced by the operation of the aileron trim drive 30, the rudder trim drive 280, and the elevator trim drive 330.

It is further believed app-arent that if the ailerons be initially manually moved and the slider 5S be also moved to unbalance the amplifier input circuit, that the coil 96 of relay 95 will be energized whereby the shaft 8l with its armature 93 is moved toward the right causing the clutch element 92 to engage the clutch face 9|! of gear 88. Gear 8S is driven in the opposite direction from gear 8S by means of intermediate pinion 89 interposed between gear 88 and the driving pinion 85. The shaft 3l which now rotates in the opposite direction also drives the shaft lili in the opposite direction. The differential arm H12 which has its clutch face IH engaged with the clutch element H2 drives the shaft IBS and through it the solid shaft .l it and slider 5S. The slider 55 is moved to rebalance the input circuit. The ailerons cause banking of the aircraft to reverse the phase of unbalance of the input of amplifier il and also cause the vertical gyro 'l0 to operate a slider in the bridge network 260 and a slider in the network 360 in the opposite direction from the rst banking movement of the aircraft. In a similar manner to that obtained before, the aileron amplifier Il, the rudder amplifier 2H, and the elevator amplier Sil will effect operation of their trim drives 8S, 286, and 380 respectively to maintain the input circuits of aileron amplifier il, rudder amplier 2l?, and elevator amplifier Sil in a balanced condition.

It is believed that the operation of the slider of the servo balance potentiometer in network 350 when the elevators are manually controlled and the subsequent operation of the trim drive 380 and that of the vertical gyro pitch poteniorneter and network 360 is apparent from a description of the operation of the aileron channel upon manual movement of the ailerons.

In like manner the operation of a rudder manually will cause initially the unbalancing of the input circuit of the rudder amplifier Il with consequent operation of rudder trim drive 2% and subsequently the directional gyro lil will unbalance the input circuits of rudder and aileron amplifiers il', 2E? with the subsequent operation of their trim drives 26d and 8i! to rebalance the input circuits of the respective amplifiers.

Under manual operation of the control surfaces therefor, the trim drives in each channel at all times operate their respective sliders to maintain the input circuits of the aileron, rudder, and elevator ampliiiers in a balanced condition irrespective of the changed attitude of the aircraft.

We may now assume that the aircraft is to be automatically stabilized on a desired heading and is in a level position with respect to the roll and pitch axes. At this time the sliders B6 of the aileron compensating potentiometer 64 and that of the directional gyro rudder potentiometer are at the mid points of their respective resistors. Similarly the slider 63 of the vertical gyro bank potentiometer El and theV slider in the rudder network 260 operated by gryo 'l0 and the slider in network 3633 operated by the vertical gyro on roll deviations are in the mid positions of their respective resistors. Similarly the slider in bridge network 36! positioned by the vertical gyro 'i0 upon movement of the aircraft about the pitch axis is also at the electrical center of its respective resistor. The aircraft is assumed to be so trimmed that all of the sliders in each amplifier control network are at the electrical centers of their respective resistors with the plane in the attitude stated. The control surfaces at this time are in their normal position.

The engage relays i6, ZIB, and 3m are considered to be operated at which time they assume the in position. The aileron servomotor lli, the rudder servomotor 2| 3, and the elevator servomotor 3M are now in brake position with respect to their respective control surfaces and maintain such surfaces in a locked position.

The aircraft is automatically maintained on the desired heading and at the desired attitude by directional gyro 74 and the vertical gyro l0 through their control of certain of the bridge elements. For example if the aircraft tends to alter its course to the left from the desired heading, the directional gyro 'M Will move the slider 6B of the aileron potentiometer 6d toward the left and the slider in the directional gyro rudder potentiometer in network 260 toward the left. This movement produces unbalance in the input circuits of amplifier l1 and 2H causing the aileron servomotor I4 and the rudder servomotor 214 to operate their sliders to rebalance the amplifier input circuits and position the ailerons and rudder. As the aircraft banks due to .the applied ailerons, the vertical gyro operates the slider 63 of the vertical gyro banking potentiometer 61, a slider in rudder bridge network 250 and a slider in bridge network 360. The signals from the vertical gyro 10 in the network 50 and 250 cause the ailerons and rudder -to be moved back toward normal position. The vertical gyro signal in network 360 causes the application of up elevator.

As the aircraft approaches a desired heading, the directional gyro '14 moves slider 66 of the directional gyro aileron potentiometer 64 and the slider of the directional gyro rudder potentiometer in network 260 back to their normal position. This unbalances the input circuits of amplifier 11 and 21'1 causing the servomotors 14 and 214 to be lreversely rotated thereby applying opposite aileron and rudder.

Due to the opposite aileron, the bank in the aircraft decreases. The decrease lvertical gyro signal in the networks 60 and 250 due to the lessening of the bank with the movement of the sliders controlled by the vertical gyro 10 back toward their normal position causes the ailerons and rudder to -be moved toward normal position. In addition the reverse movement of the slider in the up elevator potentiometer of network 360 causes the elevator to be moved back toward normal position.

The action as described is continuous in that as the aircraft approaches its normal position the bank of the aircraft decreases and the control surfaces are moved back toward normal position. When the aircraft has regained its heading, the gyro operated sliders are again at the normal position on their resistors.

When the aircraft deviates toward the opposite direction from that originally stated, a similar operation of the directional gyro potentiometers in networks 60 and 260 occurs with the sliders being moved initially in the opposite direction due to the opposite deviation. I t is believed that the subsequent operation of the s ervomotors I4 and 214 resulting from this movement, and the effect of the vertical gyro 10 on the operation of the aileron, rudder, and elevator will b e apparent from reference to the first .considered course deviation operation. As before the directional gyro initiates decrease in the bank angle.

The automatic stabilization of the aircraft with respect to the roll and pitch axes will be evident to one skilled in the art in view of the described operation of the aileron network during course deviations.

The operations of the trim drives A80, 2.80, and 380 have been considered when they were performing what is known as a centering operation or a rebalancing operation. These trim drives may also be manually operated to initiate changes in trim of the aircraft by causing initiating signals in the control circuits of the amplifier 11, 211, and 311. This operation will now be considered.

When the engage relays are operated the coils in the trim drives corresponding with coil 115 of the aileron trim drive are energized. The operation of all of the trim drives is analogous to aileron trim drive 80. With coil 115 energized, the armature 114 is attracted to thereby cause the clutch element H2 to engage the clutch face 113 of gear |08. The gear 108 is thereby driven 10 through an ep-icyclic gear train so that the shaft 108 and consequently the slider 56 is adjusted at a slower speed from the shaft 101.

If it be desired to change the trim of the aircraft about the roll axis, the pilot may operate the manually adjustable knob 131 to engage either contact or 1'2'1. The direction in which the trim of the craft is to be altered -will determine which contact 125, 127 is engaged by the switch blade 132, If contact 125 be engaged by the switch blade 132, the circuit is completed from battery 134i, lead |35, switch blade 132, contact 125, lead 122, lead 121, coil 96, to ground, and to the grounded side of battery 134. Coil 96 is thus energized and attracts armature l93 on shaft 81. Shaft 8-'1 carries the clutch element 92 which is now drivingly engaged with the clutch face 9| on gear 83. Gea-r 88 drives the hollow shaft Si and the solid shaft 101. From the shaft 101 rotation is communicated through the differential arm 102 and the epicyclic gear train to the shaft 109 and thence to shaft 1 18 which operates the slider 56. As slider 58 is operated from the trim drive, its potential with respect to that of slider 53 of the rebalancing potentiometer 51 alters. The input circuit of amplifier 11 is unbalanced, and the amplifier 1'1 causes the operation of the servomotor 14 which positions the ailerons and also operates the slider 53 to rebalance the input circuit.

Under the applied ailerons as adjusted by the servomotor 14, the aircraft begins to move about its rol-l axis. The vertical gyro 10 responds to this roll Aand operates the slider 63 of the aileron banking kpotentiometer 5I. As the aircraft tends to increase its `banked position due to the applied ailerons, the vertical gyro '10 causes the slider 63 to move along resistor B2 to unbalance the input circuit of aileron amplifier'll. This unbalance is Vof the opposite direction than that provided by the adjustment of slider 56 of the trim drive. The ailerons are therefore moved in an .opposite direction by the servomotor 14 since the amplifier input circuit has had its balance upset in an opposite direction. The ailerons are thus in oved b ack toward a normal position.

When the pilot considers that the aircraft has changed its trim about the roll axis a sufiicient amount he moves the switch blade 132 to its mid position shown. The slider 5 6 is thus no longer adjusted by the trim drive and remains in its assumed position. The ultimate positions of the sliders 63 and 56 of the vertical gyro aileron banking potentiometer and the aileron trim drive potentiometer and that of slider 53 of the .servo potentiometer are such that they set up balancing signals in the input circuit of aileron amplifier 111. The servo balance potentiometer wiper =53 has been moved back short of .the center position on its resistor 52.

The :tilt of the aircraft .about the roll axis whereby a resulting movement has been lapplied to slider 63 from vertical gyro 10 Ihas also caused the disp1.acerncnt .of the .Slider in .network .2.6.0 of the .rudder .bridge -Ileiwork The rudder amplier 2H has its input circuit unbalanced and it operates its servornotor 21.4 to position the rudder and to set up a balancing signal in network 250. The displaced rudder .tends to maintain the heading of the aircraft which would otherwise tend to change heading due to displacement of the ailerons of the aircraft.

When the pilot desired to change trim in the opposite direction about the roll axis he rotates the knob 131 to cause the switch blade 132 to engage contact |27 whereby the coil 9'| becomes energized to move the armature 94 and shaft 81 toward the left whereby the clutch element 92 is engaged with the clutch face 90 on gear 86. The slider 56 will be moved in an opposite direction to cause the opposite positioning of the ailerons so that the proper trim of the aircraft is obtained. As before the vertical gyro 1|] causes an unbalance in the input circuit of the rudder aileron amplifier 2|`| and the rudder is positioned to offset any tendency of the aircraft to turn or change its course due to the displaced ailerons which provide its new trim position about the roll axis.

In a similar way the turn axis trim control 230 may be operated to change the heading of the plane with respect to its'turn axis. This alteration in heading may be effected in either direction with respect to the stabilized position about. the turn axis which is maintained by the directional gyro 14.

Also the elevator trim control 330 may be operated to change the attitude of the aircraft about the pitch axis in either direction as desired.

Reverting to the aileron trim drive which is particularly illustrated, it is proposed to amplify the purpose in providing the two speed drive for the slider 56 of the potentiometer 54. In amplifiers of the type disclosed in the aforesaid application of Willis I-I. Gille, 447,989, and also 1n the patent to Willis H. Gille et al. 2,425,733, the amplifier operates intermittently for small signals which occur as the input circuit of the amplier approaches a balanced condition. This intermittent operation of the amplier causes automatic intermittent operation of the slider 56 when the aircraft control surfaces are being manually operated or intermittent operation of the slider 53 of the rebalancing potentiometer 5| when the aircraft is on automatic pilot. The ntermittent operation of the amplifier as the balance point is approached tends to prevent overshooting of either slider 55 or 53 when the aircraft is manually operated or automatically controlled.

With manual control of the trim drive through the control |36, however, there is no intermittent operation of the slider 56 as the aircraft approaches its desired trim condition. In order that the pilot may have ner adjustment of the slider 56 by means of the motor 8| and its driven elements a lower ratio of gears is provided by the energization of coil ||5 so that the rate of positioning of this slider 56 is decreased. It is possible then for the pilot to open the circuit between switch blade |32 and contact |25 or contact |2 when the desired trim position of the aircraft has been reached without any appreciable overrunning of the desired control point by the slider 56. A coarse and fine adjustment of the slider 56 is therefore provided by the change speed gear described.

It is now evident that there has been disclosed an improved centering arrangement for the input control circuits of a plurality of amplifiers in an automatic pilot wherein a single driving element automatically controls the operation of a plurality of centering devices in such control circuits and that such arrangement also provides for manual control of the position of such devices by means of the driving element ata reduced continuous speed to change the trim of the aircraft.

I claim as my invention:

l. Control apparatus for an aircraft comprising: motor means for altering the attitude of the aircraft about the turn, roll, and pitch axes; control means for each motor means, each control means including a balanceable circuit; position sensitive means for each circuit; operable means in each circuit for maintaining its control means balanced during attitude changes of said craft while said motor means is inoperative; a motor driven means normally operatively disengaged with all said operable means; and means controlled by each control means on unbalance thereof for effecting the operative engagement of its operable means with said motor driven means.

2. Control apparatus for an aircraft comprising: power means for operating a control surface on said aircraft; means for disabling said power means from operating said surface control means for said power means including a balanceable circuit, said control means being operative on unbalance of said circuit; means for unbalancing said circuit upon change in attitude of said aircraft; means for rebalancing said circuit by said power means; a motor means; means including variable motion transmission means rendered effective by said control means and operated by said motor means at a normal speed during attitude changes of said craft, while said power means is inoperative, to rebalance said circuit; and manual means for controlling operation of said motion transmission means by said motor means at a reduced speed while said power means is operative.

3. Control apparatus for an aircraft comprising: power means for operating a control surface on said craft; control means for said power means including a balanceable network having a plurality of signal generators and a signal combining means; means responsive to tilt for operating one signal generator to unbalance said network; means driven by said power means to operate a second signal generator to rebalance said network; means for connecting or disconnecting said power means from said control means; a third signal generator; gear transmission means including a normal and a low gear train responsive to said control means while said power means is disconnected from said control means for operating said third generator by said normal train; and manual means for controlling said transmission means and said third signal generator through said low gear train while said power means is connected.

4. Control apparatus for an aircraft comprising: power means for controlling the attitude of the craft about the turn, roll, and pitch axes; a control means for operating the power means for each axis and each control means including a balanceable network; means responsive to change in attitude of said craft about said axis for unbalancing said network to initiate operation of said control means; means driven by said power means for rebalancing said network; a motor; a plurality of change speed transmission means driven by said motor, one transmission means being associated with each network; means for affecting the balance of a network and operated by said transmission means; means for connect-v ing or disconnecting said power means with said control means; means included in each transmission means and responsive to said control means when said power means is disconnected therefrom for causing operation at one speed of said 13 balance affecting means; and manually operable means for controlling said `included means for causing operation of Said balance affecting means at another speed when said power `and control means are connected.

5. Control apparatus for an aircraft having control Isurfaces for controlling the attitude of the craft about the turn, roll, and pitch axes said apparatus comprising: a power means adapted to be Aoperatively lconnected or disconnected with each axis ycontrol surface; a pluralit of control means comprising a control means for each power means, each control means including ,a balanceable circuit; means responsive to tilt about each axis for unbalancing said control means circuits; means driven by said power means for rebalancing said circuits while said power means and control surfaces are operatively connected; a motor, a plurality of gear trains ccnnectable with said motor, means controlled by each control means while its power means is disconnected. from its control surface for connecting an associated gear train with said motor, and means driven by each gear train for affecting the balance of the circuit of its associated control means.

6. Control apparatus for an aircraft having control surfaces for controlling the attitude of the craft about a plurality of axes said appara tus comprising: a power means for each axis control surface and adapted to be connected or disconnected therefrom; a control means for each power means and including a balanceable network; means for unbalancing each network; means driven by a connected power means for rebalancing its network; a motor; a plurality of gear trains adapted to be associated or disassociated with said motor; means responsive to a control means while its power means is disconnected from a control surface to associate said motor and a gear train; and means driven by said gear train for affecting the balance of said control means network.

7. Control apparatus for an aircraft having control surfaces for controlling the attitude of the craft about a plurality of axes said apparatus comprising: a power means for each axis control surface and adapted to be connected or disconnected therefrom; a control means for each power means and including a balanceable net work; means for unbalancing each network; means driven by a connected power means for rebalancing its network; a motor; a plurality of gear trains adapted to be associated or disassociated with said motor; means responsive to a control means while its power means is disconnected from a control surface to associate said motor and a gear train; means driven by said gear train for affecting the balance of said control means network; and manually operable means for controlling said responsive means while said power means is connected for altering the trim of the craft about an axis.

8. Control apparatus for an aircraft having control surfaces for -controlling the attitude of the craft about a plurality of axes said apparatus comprising: a power means for each axis control surface and adapted to be connected or disconnected therefrom; a control means for each power means and including a balanceable network; means for unbalancing each network; means driven by a connected power means for rebalancing its network; a motor; a plurality of gear trains adapted to be operatively associated or disassociated with said motor; means responsive to a control means while its power means is disconnected from a control surface to operaiA tively associate said motor and a gear train; means driven by said gear train for affecting the balance of said control means network; means for changing the ratio of said gear train when said power means is connected with its surface; and manually operable means for controlling said responsive means while said power means is connected.

l9. A motor control system comprising: a plurality of pairs of controllers each pair comprising a main controller and a rebalancing controller; an individual power means for each pair of controllers and connected to its rebalancing controller; a control means for each power means each control means being actuated by the unbalance between a main controller and rebalancing controller and connected with its power means to reduce said unbalance.; a. motor; an ad- Justing means for each control means to shift the point of unbalance between a main controller and a rebalancing controller at which said control means :will cause said power means to operate; and means for selectively connecting each adjusting means with said motor.

1.0. A motor control system comprising: a plurality of pairs of controllers each pair comprising a main controller and a rebalancing controller; an individual power means for each pair of controllers and connected to its rebalancing controller; a control means for each power means each control means being a-ctuated by the unbalance between the main controller and rebalancing controller and connectable with its power means to reduce said unbalance; a motor; an adjusting means for each control means to shift the point of unbalance between a main controller and a rebalancing controller at which said control means will cause said power means to operate; means for operatively associating each adjusting means with said motor; and means for alternatively connecting each said control means with its power means or with said associating means.

1l. Control apparatus comprising; a plurality of amplifiers; a control circuit for each amplifier; means for unbalancing each circuit; means for rebalancing each circuit; a connectible drive means for each rebalancing means; a motor; and means controlled by each amplifier on unbalance of its control circuit for effecting connection of said motor and connectible drive means to cause operation of a rebalancing means by said motor to terminate operation of said amplifier.

Control apparatus for a dirigible craft comprising: power means for controlling the attitude of said craft about an axis; control means for operating said power means including a balanceable network having signal generating and combining means; means responsive to tilt about an axis for operating a signal generator to unbalance said network to initiate operation of said control means; means for disabling the operation of said power means by said control means; a constantly energized motor, clutch means controlled by said control means upon tilt of said craft while said power means is inoperative for operating a second signal generator from said motor at a normal speed to rebalance said network; and manual means for effecting operation of said second signal generator through said clutch from said constantly energized motor at another than said normal speed when said power means is operative by said control means.

13. In control apparatus for a dirigible craft having power means for controlling the attitude of the craft about an axis, control means for said power means including an amplier having a balanceable control circuit and operating alternatively in accordance with the direction o circuit unbalance a pair of control relays, the energization of a relay being intermittent or continuous dependent on the extent of unbalance of the control circuit, said circuit containing a plurality of signal generators and signal comsaid power means inoperative by said control means; means responsive to tilt of said craft for operating one signal generator in said circuit; means driven by said power means to operate a second generator in said circuit; a third generator in said circuit; motor operated means responsirve to closing ou? a relay of 'said control means for operating said third generator at a l0 bining means, in combination: means rendering speed dependent on relay closing duration upon tilt of said craft .while said power means is inoperative by said control means; and manual controlled means for operating said third signal generatcr from said motor operated means at a lower speed than provided by said relay closing continuously when said power means is operative.

WILLIAM L. HUNTINGTON.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,415,429 Kellogg et al Feb. 1l, 1947 2,429,642 Newton Oct. 28, 1947 FOREIGN PATENTS Number Country Date 819,170 France July 5, 1937 

